GB2117717A

GB2117717A - Pneumatic tyre tread

Info

Publication number: GB2117717A
Application number: GB08307837A
Authority: GB
Inventors: Roger Eraud
Original assignee: Compagnie Generale des Etablissements Michelin SCA
Current assignee: Compagnie Generale des Etablissements Michelin SCA
Priority date: 1982-03-22
Filing date: 1983-03-22
Publication date: 1983-10-19
Also published as: AU551982B2; IT8367314A0; AR230222A1; LU84704A1; IT1158836B; US4470443A; JPS58174003A; MA19751A1; FR2523521A1; DK129483D0; DK129483A; FI830964A0; NO830990L; SE8301525L; BE896222A; ZA831991B; GB8307837D0; EG16370A; SE8301525D0; ES278073Y

Description

1 GB 2 117 717A 1

SPECIFICATION

1 Tread for pneumatic tyres intended to travel off the highway.

This invention relates to tyres and in particular to improvements to the treads of so-called---all terrain- pneumatic tyres.

All terrain pneumatic tyres are intended for ---offroad- use and are capable of traction over ground which does not have a very firm surface, e.g. mud and melting snow. The treads of such tyres consist substantially of blocks separated one from the other in the axial direction of the pneumatic tyre by oblique or circumferential grooves. When a pneumatic tyre equipped with such a tread advances over the ground, it has a tendancy to slide owing to the lack of firmness of the surface of the ground. This sliding effect is mainly due to the poor resistance to shearing of the ground opposed to the tractive effort developed by the pneumatic tyre.

It is an object of the present invention to improve the adherence of the tread of pneumatic tyres of the type described above over soft ground.

Therefore according to the present invention there is provided a pneumatic tyre comprising a crown extended, on each side, by a sidewall terminated by a bead and a tread consisting substantially of adjacent blocks separated one from another in the axial direction of the pneumatic tyre by circumferential or oblique grooves, in which at least part of said circumferential or oblique grooves have a cross section which decreases substantially from the leading edge to the trailing edge of the blocks.

The leading edge of a block referred to 105 herein is the edge which, when the pneumatic tyre is advancing over the ground, touches the ground first; the trailing edge is that which leaves the ground last.

A groove is bounded by the walls of two adjacent blocks and the extension from block to block of the surface intended to come into contact with the ground and the base of the tread, the cross-section of a groove referred to herein is the intersection of a plane perpendicular to the median surface of the walls of the groove, with these walls, the base and the extension of the contact surface of the tread.

In the usual case, which is known per se, where the walls of the grooves according to the invention have constant inclinations, at least equal to 90', relative to the contact surface with the ground, these walls can have distances measued at the level of the contact surface with the ground, these walls can have distances measured at the level of the contact surface with the ground which decrease from walls defining the grooves are plane, these walls can form, one with each other, an angle of from 12 to 30', the angle opening in the direction of the leading edges of the blocks. These angles are measured, for example, at the level of the contact surface of the blocks with the ground.

It will readily be appreciated that the preceding definitions do not take into account the small rounded sections usually replacing the edges of the blocks comprised between the contact surface of the blocks with the ground and the base of the grooves or of the tread, and which are intended to avoid the pulling off of these edges on contact with the ground.

According to one variant of the invention, the oblique or circumferential grooves are joined by transverse grooves, which as known per se, are parallel or slightly inclined to the axial direction of the pneumatic tyre, the transverse grooves being of identical depth to the oblique or circumferential grooves and defining the blocks in circumferential direction. In addition, the oblique or circumferential grooves may have bases forming angles of from 5 to 20' with the contact surface of the blocks with the ground, which angles are open in the direction of the driving edges of the blocks. In this variant, it is also advantageous for the base of the grooves according to the invention to be arranged at the same depth as the base of the transverse grooves defining the blocks in the circumferential direction at the level of the leading edges of the blocks and to be connected to this base by rounded sections (S-shaped viewed in section) at the level of the trailing edges of the blocks.

In a further variant, at least part of the circumferential or oblique grooves are arranged axially so as to open on the block following them in the circumferential direction of the pneumatic tyre. in fact, the main idea of the invention lies in the convergence, between the leading edge and the trailing edge of the blocks, of the walls and/or of the base of the oblique or circumferential grooves sep- arating these blocks in the axial direction in relation to the flow, for example, of the loose soil, in these grooves. The section offered by the grooves to this flow therefore diminishes from the leading edges to the trailing edges of the adjacent blocks in the axial direction. When these circumferential or oblique grooves, i.e. forming on average an angle less than or, preferably, very much less than 45' with the circumferential direction, open at the level of the trailing edges of the blocks according to the above variant, in a quasitransverse groove facing another block, the compacting of the muddy flow is further improved, since the flow is divided and the direction of the partial flows varies abruptly by 90' and more.

So as to take into account the possible differences of nature and properties of soils of loose surface, the reduction of the section offered by the grooves to the flow of these 2 GB 2 117 717A 2 different loose soils is such that the section of the groove corresponding to the exit edges of the blocks is comprised between 0.35 and 0.60 times the section of the same groove corresponding to the leading edges.

The invention will now be described with reference to the accompanying drawings, in which:

Figure 1 represents a partial plan view of a tread of a pneumatic tyre according to the 75 invention, and Figures 2 to 4 represent plane sections made along the lines 11, Ill, and W respec tively shown on Fig. 1.

The tread of Fig. 1 is formed by blocks 10 to 15. Three blocks 10 to 12, adjacent in the axial direction, form a row and are separated from the adjacent rows of blocks 13 to 15 in the circumferential direction by grooves 16, 17 which have a mean inclination in the 85 transverse direction. In the first row, the adja cent blocks 10 to 12 each have a front leading edge 10 1, 111, 121 which touches the ground first, taking into account the arrow F indicating the direction of rotation of the pneumatic tyre. These blocks 10 to 12, each leave the ground by their rear trailing edge 102, 112, 122. In the second row of blocks 13 to 15 (partially shown), separated in the circumferential direction from those blocks 10 to 12 of the first row by the quasi-transverse groove 17, the blocks 13 to 15 attack the ground by their leading edges 131, 141, 151 contiguous to the quasi-transverse groove 17.

In each row of blocks 10 to 12, 13 to 15 which are axially adjacent, circumferential grooves 2, 3, 4, 5 according to the invention separate the median blocks 11 and 13 from the lateral blocks 10, 12 and 14, 15 respectively. According to a preferred variant, the grooves 2, 3 according to the invention of a row of blocks 10 to 12 are staggered axially in relation to the grooves 4, 5 of the following row of blocks 13, 14, 15. In this way, the grooves 2, 3 of a row 10 to 12 open into the quasi-transverse groove 17 below the trailing edges 102, 112, 122, of blocks 10, 11, 12 but facing the leading edges 131, 141, 151 or blocks 13, 14, 15 of the following row.

Figs. 3 and 4 show cross-sections via planes Ill and IV of the groove 3 according to the invention, situated between a median block 11 and the adjacent lateral block 10. In this example, the median plane of this groove 3 is the plane 11 parallel to the equatorial plane of line XX' of the pneumatic tyre. The longitudinal section of this groove 3 along the line 11 in Fig. 1 is represented in Fig. 2. The walls 30, 31 of this groove 3 are plane and form angles 13 (Fig. 1) of 8' with the circumferential direction and angles y (Figs. 3 and 4) of 100' with the contact surface 33 with the ground.

The cross-section of Fig. 3 is closer to the 6 5 leading edges 10 1, 111 of the blocks 10, 11. According to the invention, the area of this section is greater than that of the crosssection of Fig. 4 made at a greater distance from the leading edges 101, 111.

Fig. 2 is a section of groove 3 according to the invention along the median plane 11 of this groove. According to the invention, the area of cross-sections Ill and IV diminishes from cross-section Ill to crosssection IV, i.e. in the direction of the trailing edges 102, 112. This decrease results both from the convergence of the lateral walls 30, 31 of groove 3 and from the fact that the base 32 of groove 3 forms an angle a (Fig. 2) of an inclination of 7' with the parallel to the rolling surface 33 of block 10, i.e. the tread. This angle opens in the direction of the leading edges 10 1, 111 of blocks 10, 11.

The point 35 of the inclined base 32, closest to the contact surface 33 of the tread with the ground, is situated approximately flush in the circumferential direction with the trailing edges 102, 112 of the adjacent blocks 10, 11. This point 35 of maximum radial narrowing of the section of groove 3 coincides approximately with the maximum axial narrowing 37 of the section of groove 3. A very short rounded zone 36, in the shape of an S, connects the point 35 of maximum raidal narrowing to the base 170 of the groove below contiguous to the trailing edges 102, 112 of the adjacent blocks 10, 11.

Claims

1. A pneumatic tyre comprising a crown extended on each side, by a sidewall terminated by a bead and a tread consisting substantially of adjacent blocks separated from one another in the axial direction of the pneu- matic tyre by circumferential or oblique grooves, in which at least part of said circumferential or oblique grooves have a crosssection which decreases substantially from the leading edge to the trailing edge of the blocks.

2 A pneumatic tyre as claimed in Claim 1, in which said grooves have walls which have a constant inclination, at least equal to 90' relative to the contact surface with the ground, and are separated by a distance which decreases substantially from the leading edge to the trailing edge of the adjacent blocks.

3. A pneumatic tyre as claimed in Claim 2, in which said grooves have walls which are plane and which form with each other an angle of from 12 to 30' said angle opening in the direction of the leading edges of the blocks.

4. A pneumatic tyre as claimed in any preceding claim, in which said grooves are connected by transverse grooves which are parallel or slightly inclined to the axial direction, the transverse grooves being of identical depth of said circumferential or oblique 1 t J1 3 GB2117717A 3 grooves and define the blocks in the circumferential direction.

5. A pneumatic tyre as claimed in Claim 4, in which said grooves have a base forming an angle of from 5 to 20' with the contact surface of the blocks with the ground, which angles are open in the direction of the leading edges of the blocks, the bases of these grooves being arranged at the same depth as the base of the grooves defining the blocks at the level of the ing edges of the blocks, and connected by rounded zones to this base at the level of the trailing edges of the blocks.

6. A pneumatic tyre as claimed in any preceding claim, in which at least a part of the grooves are arranged axially so as to open onto the leading edge of a block in the row of blocks following them in the circumferential direction of the pneumatic tyre.

7. A pneumatic tyre as claimed in any preceding claim, in which the section of the groove corresponding to the trailing edge is comprised between 0.35 and 0.60 times the section of the same groove corresponding to the leading edge.

8. A pneumatic tyre substantially as herein described with reference to the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd-1 983. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.